Injection is Tapestry's way of making a dependency – such as a resource, asset, component, block or service – available in a page, component, mixin or service class.
| Div | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| ||||||||||
|
Injection is a key concept in Tapestry, and it is used in several different but related ways, listed below.
Injection in Tapestry IOC Services
Main Article: Tapestry IoC Overview Injection in Detail
The Tapestry IoC container makes use of injection primarily through constructors and via parameters to service builder methods.
...
For field type Block, the value of the Inject annotation is the id of the <t:block> element within the component's template. Normally, the id of the block is determined from the field name (after stripping out any leading "_" and "$" characters):
| Code Block | ||||
|---|---|---|---|---|
| ||||
@Inject private Block foo; |
Where that is not appropriate, an @Id annotation can be supplied:
| Code Block |
|---|
@Inject @Id("bar") private Block barBlock; |
The first injection will inject the Block with id "foo" (as always, case is ignored). The second injection will inject the Block with id "bar".
...
A very common example occurs when a component needs access to its resources. The component can define a field of the appropriate type and use the @Inject annotation without a value:
| Code Block | ||||
|---|---|---|---|---|
| ||||
@Inject private ComponentResources resources; |
Tapestry uses the type of the field, ComponentResources, to determine what to inject into this field.
...
When the @Path annotation is also present, then the injected value (relative to the component) will be a localized asset.
| Code Block | ||||
|---|---|---|---|---|
| ||||
@Inject @Path("context:images/top_banner.png") private Asset banner; |
Symbols in the annotation value are expanded.
...
Here, a custom EmployeeService service is injected, but any custom or built-in service may be injected in the same way.
| Code Block | ||||
|---|---|---|---|---|
| ||||
@Inject private EmployeeService employeeService; |
A large number of services are provided by Tapestry. See the following packages:
| Wiki Markup |
|---|
{float:left|width=15em} * [Core Services|http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/package-summary.html] * [AJAX Services|http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/ajax/package-summary.html] * [Assets Services|http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/assets/package-summary.html] * [Dynamic Component Services|http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/dynamic/package-summary.html] {float} |
| Wiki Markup |
|---|
{float:left|width=15em} * [JavaScript Services|http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/javascript/package-summary.html] * [Link Transformation Services|http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/linktransform/package-summary.html] * [Message Services|http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/messages/package-summary.html] * [Component Metadata Services|http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/meta/package-summary.html] {float} |
| Wiki Markup |
|---|
{float:left|width=15em} * [Page Loading Services|http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/pageload/package-summary.html] * [Security Services|http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/security/package-summary.html] * [Template Services|http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/templates/package-summary.html] * [Class Transformation Services|http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/transform/package-summary.html] {float} |
| Wiki Markup |
|---|
{float:left|width=15em} * [Tapestry IOC Services|http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/ioc/services/package-summary.html] * [Tapestry IOC Cron Services|http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/ioc/services/cron/package-summary.html] * [Kaptcha Services|http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/kaptcha/services/package-summary.html] * [File Upload Services|http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/upload/services/package-summary.html] {float} |
| HTML |
|---|
<div style="clear:both"></div> |
Explicit Service Injection
Here, a specific object is requested. A @Service annotation is used to identify the service name.
| Code Block | ||||
|---|---|---|---|---|
| ||||
@Inject @Service("Request") private Request request; |
This is generally not necessary; you should always be able to identify the service to be injected just by type, not by explicit id. Explicit ids have the disadvantage of not being refactoring-safe: this won't happen with the Request service, but perhaps in your own code ... if you rename the service interface and rename the service id to match, your existing injections using the explicit service id will break.
...